1. Field of the Invention
The present invention relates to processes for forming beam-leaded microelectronic chip structures and, more particularly, to batch processes wherein a plurality of interdigitated beam leads of a preferred metal such as aluminum or gold are formed simultaneously on a wafer or substrate comprising a plurality of pre-fabricated microelectronic devices, each such device having pre-fabricated metallized contact pads of substantially the same preferred metal as is used to form the beam leads.
2. Description of the Prior Art
Batch processes for providing microelectronic circuits and similar devices with beam leads have been practiced for a significant period of time. Most such devices use aluminum metallization internally. However, for the relatively thick metallic films required to be deposited for beam leads, vacuum deposition techniques heretofore used for aluminum have not been satisfactory. For example, the deposition techniques have been relatively slow thereby permitting aluminum oxide to contaminate the aluminum. The aluminum is thereby caused to be relatively brittle and to have relatively high resistivity. On the other hand, high purity gold having good physical and electrical characteristics, as well as high resistance to corrosion, can be deposited to any desired thickness by electroplating. For this reason, gold has been the desired metallization for forming beam leads by batch processing.
However, gold beam leads should not be formed to have a direct interface with aluminum metallization. By reason of interdiffusion of these two metals, intermetallic compounds which are both brittle and highly resistive will evantually form and the integrity of such an interface will be degraded or destroyed. To avoid using gold directly on aluminum, the common practice has been to form indirect connections from the semiconductor regions of, for example, bipolar transistors within the device to gold beam leads through composites or laminates which are free of aluminum. One layer of the composite provides a relatively stable low-resistance ohmic contact adhering to the semiconductor material while another layer of a barrier material, e.g., platinum, affixes the gold while preventing the formation of deleterious interdiffusion products. While some manufacturers have successfully produced bipolar devices, for example, with such processes, the use therein of rf sputtering techniques for depositing one or more of the layers for the composite renders these processes undesirable for use with MOS devices. The radiation commonly generated by rf sputtering tends to adversely affect the characteristics of the latter type of circuitry.
There remains a need for a high-yield batch process for affixing beam leads to microelectronic devices which is relatively simple to practice effectively for a variety of circuitry.